- Like what you've got: probably stick with it. As maligned as the camera was in some respects, it was ahead of its time in others, and the 14mp sensor still delivers good results. You have two worries, however: parts are getting scarce, so the camera may not be repairable if something happens to it, and what software support there was for it is frozen where it was. Eventually, companies are going to stop supporting the Kodak raw format.
- Dislike what you've got: You have two nice choices for moving up: the D610 and D750. Both give you a better camera body, many more pixels, and keep you in FX.
- Upgrade to mirrorless: Zf, Z6III, or Z7II. You opted for an oddball choice originally, so you’d probably consider the oddball choices again.